The present invention relates to subterranean stimulation operations and, more particularly, to processes and apparatus for improving the reliability of pinpoint stimulation operations.
To produce hydrocarbons (e.g., oil, gas, etc.) from a subterranean formation, well bores may be drilled that penetrate hydrocarbon-containing portions of the subterranean formation. The portion of the subterranean formation from which hydrocarbons may be produced is commonly referred to as a “production zone.” In some instances, a subterranean formation penetrated by the well bore may have multiple production zones at various locations along the well bore.
Generally, after a well bore has been drilled to a desired depth, completion operations are performed. Such completion operations may include inserting a liner or casing into the well bore and, at times, cementing a casing or liner into place. Once the well bore is completed as desired (lined, cased, open hole, or any other known completion) a stimulation operation may be performed to enhance hydrocarbon production into the well bore. Where methods of the present invention reference “stimulation,” that term refers to any stimulation technique known in the art for increasing production of desirable fluids from a subterranean formation adjacent to a portion of a well bore. Examples of some common stimulation operations involve hydraulic fracturing, acidizing, fracture acidizing, and hydrajetting. Stimulation operations are intended to increase the flow of hydrocarbons from the subterranean formation surrounding the well bore into the well bore itself so that the hydrocarbons may then be produced up to the wellhead.
Conventional pinpoint stimulation techniques may be susceptible to movements of the hydrajetting tool, which can generally reduce the tool performance. These movements may be caused by a number of factors, including wellbore geometry and tubing movement due to thermal and pressure effects. Further movement may occur around the hydrajetting tool due to the effects of turbulence, vibration, pressure related piston effects and jet thrust. Longer jetting times may compensate for this reduction in tool performance. However, the increase in jetting times may not be desirable.
One suitable hydrajet stimulation method, introduced by Halliburton Energy Services, Inc., is known as the SURGIFRAC and is described in U.S. Pat. No. 5,765,642. The SURGIFRAC process may be particularly well suited for use along highly deviated portions of a well bore, where casing the well bore may be difficult and/or expensive. The SURGIFRAC hydrajetting technique makes possible the generation of one or more independent, single plane hydraulic fractures. Furthermore, even when highly deviated or horizontal wells are cased, hydrajetting the perforations and fractures in such wells generally result in a more effective fracturing method than using traditional perforation and fracturing techniques.
During the SURGIFRAC process, which uses the Bernoulli principle to achieve fluid diversion between fractures, the primary flow goes to the fracture while the secondary, leakoff flow, is supplied by the annulus. In some instances, such as in long horizontal well bores, a large number of fractures may be desired. The formation of each fracture results in some additional leakoff. Consequently, with the increase in the number of fractures, the amount of the secondary, leakoff flow increases and eventually may exceed the amount of the primary flow to the fracture. The increased fluid loss may reduce the efficiency of the operations and increases the cost.
Another suitable hydrajet stimulation method, introduced by Halliburton Energy Services, Inc., is known as the COBRAMAX and is described in U.S. Pat. No. 7,225,869, and is applicable to vertical, deviated, and horizontal wells, which is incorporated herein by reference in its entirety. The COBRAMAX process may be particularly well suited for use along highly deviated portions of a well bore. The COBRAMAX technique makes possible the generation of one or more independent hydraulic fractures without the necessity of zone isolation, can be used to perforate and fracture in a single down hole trip, and may eliminate the need to set mechanical plugs through the use of a sand plug.
The COBRAMAX process involves isolating the hydrajet stimulated zones from subsequent well operations. The primary fluid diversion of the previous regions in the COBRAMAX process is achieved by placing sand plugs in the zones to be isolated. The placement of sand plugs, particularly in horizontal well bores, may require a prescribed flow rate, which may be difficult to achieve when using surface pumping equipment.
Other methods for improving reliability of pinpoint stimulation operations are described in U.S. patent application Ser. No. 12/244,547 filed on Oct. 2, 2008, which is hereby incorporated by reference as if fully reproduced herein.